Block (such as stone or grass, but not limited to) changes when entity is placed on it.

Block (such as stone or grass, but not limited to) changes when entity is placed on it.
What I expected to happen was the block (it was grass and sand block that i saw it happen on twice in a 5 minute period)
to not change.

What actually happened was transformed, if you will, to a different entity. I was a little frazzled when it happened the first time.

1.not possible to tell an exact step by step but, i placed a railroad track (i also did a switch and a red stone piece) on the grass block (it was in the swamp but it doesn't have to be)and it changed to sand